Separation, washing and determination of analytes tagged with magnetic particles

A method for determining the presence of a material of interest (MOI) in a sample, in which the MOI is,

• a). a blood group antigen present on a red blood cell, in said sample, or
• b). an antibody in said sample that binds to a blood group antigen present on a red blood cell,
• which method comprises,
• A. preparing a reaction mixture of a) or b) with a binding partner for the MOI whose presence is sought to be determined, said, binding partner, in the case when the MOI is as described in a), being an antibody which binds with the red blood cell group antigen of a) above, or,
• in the case where the MOI is an antibody as described in b) above, said binding partner of the MOI being the blood group antigen present on a red blood cell as described in b) above, wherein said red blood cells are either directly tagged with magnetic particles or indirectly tagged through a linkage to the red blood cell with a red blood cell binding agent such as a lectin tagged with magnetic particles, whereby the magnetically tagged red blood cell particles react with the MOI if present to produce a reacted magnetic particle/MOI complex, or do not so react if the MOI is not present and remain as unreacted magnetically tagged red blood cell particles,
• B. providing a capture vessel comprising a paramagnetic capture element, and a wash fluid which optionally comprises an anti-species globulin such as Coombs serum, either in the fluid or on the element or both,
• C. introducing the reaction product mixture of step A into the capture vessel of step B,
• D. applying a magnetic force to the paramagnetic capture element whereby the paramagnetic capture element is rendered magnetic by said magnetic force, and the reacted magnetically tagged particles/MOI complex and any unreacted magnetically tagged red blood cell particles from the reaction mixture are moved into and through the wash fluid,
• E. allowing the magnetically tagged particles to form a deposit on the paramagnetic capture element and thereafter discontinuing application of the magnetic force after deposition occurs,
• F. applying a disruptive force to the deposit on the paramagnetic capture element to determine if the deposit is a strongly adhering deposit or large agglutinate, combined with or without anti-species globulin, thus indicating a positive result for the presence of the MOI, or a weakly adhering blood cell antigen deposit thus indicating a negative result for the presence of the MOI.